"We keep waiting, we keep praying", Ratih Wardhani, whose brother Major Wisnu Subiyantoro among the crew, told the BBC.
Even if the submarine were to be located, rescuing the vessel and its crew will be challenging, Frank Owen, director of the Submarine Institute of Australia, told NBC News. Rescuers made similar massive searches in the previous two days.
Meanwhile, two Australian ships were heading for the search area including a support ship and a frigate with sonar capabilities, the defence department said in a statement.
Singapore's MV Swift Rescue - a submarine rescue vessel - was expected later Saturday.
When the commander of the training task force tried to authorize the firing drill 25 minutes later, communication with the submarine could not be established.
President Joko Widodo on Thursday said in an online address that the crew was the government's top priority and asked the public to "pray for this search and rescue to be carried out". "To the family of the crew members, I can understand your feelings and we are doing our best to save all crew members on board".
The search focused on an area near the starting position of its last dive where an oil slick was found but there is no conclusive evidence so far the oil slick was from the sub.
Judge admonishes Maxine Waters’ comments on Chauvin murder trial as ‘abhorrent’
I don't know whether it's in the first degree, but as far as I'm concerned it's first degree". She also said: "We've got to get more confrontational.
Margono, the navy cheif, had said oil could have spilled from a crack in the submarine's fuel tank or the crew could have released fuel and fluids to reduce the vessel's weight so it could surface.
Navy chief of staff Admiral Yudo Margono said an unidentified object with high magnetism was located at a depth of 165 to 330 feet, with officials hoping it was the submarine.
The navy has said it believes the submarine sank to a depth of 2,000-2,300 feet, much deeper than its collapse depth - the depth at which water pressure would be greater than the hull could withstand. The vessel's collapse depth was estimated at 200 metres (655 feet) by a South Korean company that refitted the vessel in 2009-2012.
The cause of the disappearance is still uncertain.
But the passing of Saturday's oxygen deadline was likely to mean the Southeast Asian archipelago would be added to a list of countries struck by fatal submarine accidents. Most of the Kursk's crew died instantly but some survived for several days before suffocating.
The submarine - one of five in Indonesia's fleet - disappeared early Wednesday during live torpedo training exercises off the Indonesian holiday island.
But in 2005, seven men aboard a Russian mini-sub were rescued almost three days after their vessel became snagged by fishing nets and cables in the Pacific Ocean. They had only six hours of oxygen left before reaching the surface.
While warships, planes and hundreds of military personnel took part in a frantic search for the KRI Nanggala 402, authorities had said the German-built craft was equipped with enough oxygen for only three days after losing power.